I am trying to install properly Twitter Bootstrap in my current ember-cli project. I did install bootstrap with bower :
bower install --save bootstrap
$> bower install --save bootstrap
Afterwards add following two lines to your ember-cli-builds.js (or Brocfile.js if you are using an older version of Ember.js):
app.import(app.bowerDirectory + '/bootstrap/dist/js/bootstrap.js');
app.import(app.bowerDirectory + '/bootstrap/dist/css/bootstrap.css');
And voilà, ready to go!
updated 08/18/2015: adapted to new scheme introduced in Ember.js 1.13